earlier incarnations of The Master?

When The Master first appears he's on one of his last regenerations, so why not show earlier versions of The Master interacting with later versions of The Doctor in future stories? That would be a sensible way to have more of the character if they really wanted to keep him dead (not that they should, since him being able to not regenerate was one of manyridiculous plot devices in that episode).

The idea is interesting but the chances of setting up a paradox is likely.

If early incarnations of the Master take on later incarnations of the Doctor, then will slightly later versions of that early Master know he does not win another confrontation with the Doctor, since he took on such a later Doctor version?